The present invention is directed to oxymethylene homopolymers and copolymers. More specifically, the present disclosure pertains to polyoxymethylene compositions which posses thermal stability and resistance to mold and die deposits.
The prior art has been extensively developed in the field of oxymethylene homopolymers and copolymers which are thermally stable and which are present in compositions that contain additives such as polyamides or superpolyamides.
In Alsup et al. U.S. Pat. No. 2,993,025 issued July 18, 1961, high thermal stability is provided into a polyoxymethylene composition by incorporation of 0.001% to 50% by weight of a superpolyamide such as nylons in which is present the carbonamide linkage ##EQU1## with R defining hydrogen, alkyl or alkoxy. The superpolyamide has a preferred degree of polymerization of about 100 to 200 and upon hydrolysis yields monomeric compounds of (1) mixtures of dicarboxylic acids and diamines and/or (2) omegaaminomonocarboxylic acids.
In Herman et al. U.S. Pat. No. 3,131,165 issued Apr. 28, 1964, is found a teaching of stabilizing formaldehyde polymers with primary and secondary amides of polybasic acids including oxalic acid diamide and compounds of the formula R(CONHR.sub.1).sub.n with R representing a polyvalent alkyl, cycloalkyl, aryl, aralkyl or a heterocyclic radical and the substitution products of these radicals, R.sub.1 is a hydrogen atom or an alkyl or cycloalkyl radical having a molecular weight of up to 500, or the substitution products of these radicals, and n represents a whole number of at least 2 and preferably 2 to 4.
In Fourcade et al., U.S. Pat. No. 3,306,953 issued Feb. 28, 1967, is disclosed stabilization of polyoxymethylene by addition of a 0.5 to 2.0% by weight of a polyamide obtained by the condensation of a dimer or trimer of an unsaturated fatty acid containing at least 10 carbon atoms with at least a stoichiometric quantity of a diamine or a triamine.
In O'Brien et al. U.S. Pat. No. 3,444,265 issued May 13, 1969, is disclosed an oxymethylene copolymer composition with improved high temperature stability by incorporation of a thermoplastic linear polycarbonamide and a solid fusible diphenylamine-acetone condensation product. Within the disclosure of the types of linear polyamides which are suitable are those having a molecular weight above 1000 although only nylon is demonstrated.
In British Patent Specification No. 1,346,026 published Feb. 6, 1974, is set forth formation of a polyacetal composition having high resistance to thermal decomposition and discoloration at high temperatures. Disclosed in the composition is a polyamide which is a polycondensation product of (A) H.sub.2 NRNH.sub.2 where R is an aliphatic, alicyclic, or aromatic hydrocarbon group or groups of hydrocarbons combined by oxygen or sulfur atoms; (B) XOCCH.sub.2 COX where X are hydroxyl groups, halogen atoms or lower alkoxy groups and (C) YCH.sub.2 COX where X is as previously defined and Y is a cyano or carbamoyl group. The ratio of components (A), (B), (C) is not limited but it is preferable that each of (A) and (B) is in an amount of 1 to 30 moles with respect to 1 mole of (C). Molecular weights of the order of 300 to 100,000 and preferably 450 to 5,000 are disclosed in relationship to the polyamide.